A coalition is an alliance between entities, during which they cooperate in joint action, each in their own self-interest. This alliance may be temporary, or a matter of convenience. A coalition thus differs from a more formal covenant. See Axelrod's book, The Evolution of Cooperation.

See also: united front

Political science

• A coalition government, in a parliamentary system, is a government composed of a coalition of parties.

• In Australia, the Coalition is also used to refer to an alliance of three parties (the Liberals, Nationals and Country Liberals) existing in federal politics since 1922.

• In international relations, the term Coalition of the Willing refers to an ad hoc grouping of nations united for a specific purpose, often highly diverse, characterized by such a high degree of uncommonalities that many would perceive them as being ordinarily unlikely to unite; it also indicates the fact the historical ties may no longer be in operation, and the coalition members, instead, are joined by a new intention, not necessarily prior bonds. The term Coalition of the Willing term was employed during the 2003 war in Iraq lead by the United States and its allies

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Mathematics

Coalitions can be studied as games. The Nash equilibrium defines conditions where rational players can benefit other players in the coalition.

Computer science

In the computer field, and in the study of cognition, the entities can be called agents or daemons. By definition, agents can form coalitions.

Fiction

In the fictional Star Fleet Universe as represented in the range of games from Amarillo Design Bureau Inc. as well as the first two Star Fleet Command games (and the Orion Pirates stand-alone addon for Starfleet Command II) from Taldren, the Coalition is the alliance of the Klingon Empire and the Lyran Star Empire - eventually also including the Romulan Star Empire - which fought together against the Alliance in the General War, the Klingons and Lyrans having been allied in the previous Four Powers War from Y158-Y162.

Military

In military usage, coalition is used to refer to any operation involving more than one country unified under a single command.